from django.utils import timezone
from modules.invoicing.models import Invoice, InvoiceItem
from modules.invoicing.utils import generate_invoice_number
from django.db import transaction
from django.contrib.auth import get_user_model
from rest_framework.exceptions import ValidationError
import logging
from decimal import Decimal
from modules.invoicing import tasks  # premještamo ovdje ako treba

logger = logging.getLogger(__name__)

class InvoiceService:
    @staticmethod
    def create_full_invoice(user=None, **validated_data):
        # 1. Obavezno dohvati stavke
        items_data = validated_data.pop('items', [])

        fields_to_remove = ['amount', 'creator', 'invoice_number']
        for field in fields_to_remove:
            validated_data.pop(field, None)

        # 2. Sigurna provjera korisnika
        if not user:
            User = get_user_model()
            try:
                user = User.objects.get(username="paperless_bot")
            except User.DoesNotExist:
                raise ValidationError("Sistemski korisnik 'paperless_bot' ne postoji.")

        with transaction.atomic():
            # 3. Računanje iznosa (sigurno rukovanje s items_data)
            total = sum(Decimal(item['quantity']) * Decimal(item['unit_price']) for item in items_data)

            # 4. Kreiraj fakturu
            invoice = Invoice.objects.create(
                **validated_data,
                amount=total,
                creator=user,
                invoice_number=generate_invoice_number()
            )

            # 5. Kreiraj stavke
            for item_data in items_data:
                InvoiceItem.objects.create(invoice=invoice, **item_data)

            # 6. Pokreni task nakon commit-a
            transaction.on_commit(lambda: tasks.process_paperless_document_task.delay(invoice.id))

        return invoice

    @staticmethod
    def create_invoice_entry(data, user=None):
        """
        Kreira financijski zapis (transaction) na temelju validated data.
        Očekuje se da data['invoice'] može biti instanca ili PK.
        """
        from modules.invoicing.models import InvoiceTransaction, Invoice

        invoice = data.get("invoice")
        if isinstance(invoice, int):
            invoice = Invoice.objects.get(pk=invoice)
        elif hasattr(invoice, "pk") is False:
            raise ValidationError("Nevažeći invoice.")

        amount = data.get("amount")
        payment_date = data.get("payment_date", None)
        work_order = data.get("work_order")

        tx = InvoiceTransaction.objects.create(
            invoice=invoice,
            work_order=work_order,
            invoice_number=invoice.invoice_number,
            amount=amount,
            payment_date=payment_date or timezone.now()
        )
        return tx